A security flaw in the recent iOS 6.1 patch has been discovered by users and allows them to bypass your lockscreen. The flaw was first documented by YouTube user videosdebarraquito, and involves making and immediately cancelling an emergency call and pressing and holding down the power button twice. The good news is that Apple is already aware of this issue and is working hard on a software patch to fix this issue.
Source: videosdebarraquito